The present invention relates generally to electronic devices that have an active organic layer and at least an electrode having a structure that mitigates the adverse effects of defects resulting from the construction of such devices. In particular, the present invention relates to structures of at least an electrode, which structures mitigate effects of short circuits in such devices.
Organic electroluminescent devices (“OELDs”), which have been recently developed, can provide an attractive and more suitable alternative to inorganic electroluminescent devices in many applications, such as large-area illumination.
An OELD is typically a thin film structure formed on a substrate such as glass or transparent plastic. A light-emitting layer of an organic electroluminescent (“EL”) material and optional adjacent organic semiconductor layers are sandwiched between a cathode and an anode. The organic semiconductor layers may be either hole (positive charge)-injecting or electron (negative charge)-injecting layers and also comprise organic materials. The material for the light-emitting layer may be selected from many organic EL materials that emit light having different wavelengths. The light emitting organic layer may itself consist of multiple sublayers, each comprising a different organic EL material. State-of-the-art organic EL materials can emit electromagnetic (“EM”) radiation having narrow ranges of wavelengths in the visible spectrum. Unless specifically stated, the terms “EM radiation” and “light” are used interchangeably in this disclosure to mean generally radiation having wavelengths in the range from ultraviolet (“UV”) to mid-infrared (“mid-IR”) or, in other words, wavelengths in the range from about 300 nm to 10 micrometers. To obtain white light, prior-art devices have incorporated closely arranged OELDs emitting blue, green, and red light. These colors are mixed to produce white light. An alternate scheme to produce white light is set forth in U.S. Pat. No. 5,294,870; which describes an organic EL multicolor display device comprising an organic EL source emitting blue light with green- and red-emitting fluorescent materials applied to different subpixel areas. This device emits different colors from the different subpixel areas by color shifting with the green- and red-emitting fluorescent materials. However, the manufacture of such microdevices is complex and requires sophisticated technologies; and, thus, increases cost. Moreover, for general lighting purposes, large-area OELDs must be fabricated. The manufacture of defect-free large-area OELDs is a challenge. Typically, a defect in the fabrication, such as one that allows a short circuit, would render the whole device inoperative and darkened.
Therefore, it is very desirable to provide organic electronic devices, the operation of which is more tolerant to fabrication defects. It is also very desirable to provide organic electronic devices that remain operative even when there are microscopic short circuits in the originally made devices.